A bioreactor is a device or system that supports a biologically active environment. For example, a bioreactor may be a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. The chemical process may be aerobic or anaerobic and the system may be closed or open. Bioreactors may range in size from liters to cubic meters.
A photobioreactor (PBR) is a bioreactor which incorporates some type of light source. Photobioreactors are used to grow small phototrophic organisms such as cyanobacteria, algae, or moss plants. These organisms use light through photosynthesis as their main energy source and do not require sugars or lipids as energy source. The term PBR is commonly used to define a closed system in which the walls of the container are translucent. This configuration is selected so that sunlight can penetrate the walls of the container. A PBR may also be an open system such as an open tank or pond but this presents a greater challenge for delivery of appropriate levels of light to sustain the photoreactions.
In both cases, open systems and closed systems, the level of light delivered is critical to the efficiency of the bioreactor. It is desirable to use sunlight as the primary source of photo energy as it is free and abundant. However, if too little light is delivered the organisms die or too little photosynthesis occurs to be useful. On the other hand, if too much sunlight is delivered it is detrimental to the organisms. It has been reported that sunlight is 4 to 5 times too intense for most species of micro-algae.
It is expected that for enhanced efficiency sunlight needs to be diluted and evenly distributed throughout the photobioreactor. Known photobioreactors, such as that described in International Patent Publication WO 2010/132955, describe systems for collecting and intensifying sunlight but do not adequately address distributing the sunlight in the photobioreactor. Other known arrangements, such as described in International Patent Publication WO 2010/077638, merely use a cylindrical waveguide to transport the collected sunlight to a greater depth in a photobioreactor container or open pond, they do not address even distribution of the sunlight.
Carbon emissions have become an issue in many countries. In recent years a number of countries have introduced carbon trading schemes in an effort to encourage emmitters to reduce carbon emissions. These schemes have the potential to improve the economic viability of the commercial scale use of photobioreactors.